Generally, such spotlights comprise, in addition to a reflector and a glass which together delimit a volume in which an electric light bulb is located, a shell surrounding the reflector at a distance therefrom and fixed to the reflector in the immediate vicinity of its junction with the glass, said shell being provided with a member for mounting the spotlight on a support.
The use of such a structure which is commonly found in the prior art has the advantages of providing mechanical protection for the reflector against shocks such as flying chips, and also of avoiding direct fixing between the mounting member and the reflector, since such fixing is a priori incompatible with the thermal expansions applied to the various parts of such a spotlight when put into use. Generally speaking such thermal expansions would tend to loosen the mounting member with respect to the reflector, unless the mounting member would be strongly secured thereto to; in such a case, the attachment of the mounting member on the reflector would localy impede the thermal expansion of the reflector, leading to difficulties in gauging such expansion and thus compensating in advance the consequences thereof on the mean direction of the light beam of the spotlight when it is in use, and on the distribution of light within said beam.
However, the presence of a shell in prior art spotlights has the effect of confining a volume of air around the reflector, and the temperature of this volume of air rises considerably when the spotlight is in operation. As a result there is considerable thermal expansion not only of the reflector but also of the shell and this means that compensation for the effects of thermal expansion in order to avoid significantly changing the average direction in which the light beam is projected and also to avoid changing the distribution of light flux within said beam, requires complex calculations to be performed which take account both of the shell and of the reflector. The net result is an added degree of uncertainty by virtue of the presence of two separate items whose thermal behavior must be compensated for.
Further, adding a shell to a reflector increases the overall price of the spotlight.
An object of the present invention is to remedy these drawbacks by omitting the shell since its function of providing mechanical protection to the reflector can equally well be provided by reinforcing the thickness of the reflector, and also by providing means for mounting the spotlight on a support, which means are directly connected to the reflector while still allowing thermal expansion there of as required. Another object of the invention is to render said fixing means substantially insensitive to variations of temperature over the normal operating range of temperatures thereby the direction in which the light beam points and on the distribution of light flux within the beam when the spotlight is in operation, the only thermal expansions that need taking into account being those which concern the reflector.